1. Field of the Invention
The present invention relates to a technical field of mode transfer control apparatus and method for a hybrid vehicle having a fixed transmission gear ratio mode by an engagement of an engagement element in addition of a continuously variable transmission gear ratio as a steady-state mode selected when the vehicle is started or traveled.
2. Description of the Related Art
A Japanese Patent Application First Publication No. 2003-34153 published on Feb. 4, 2003 exemplifies a previously proposed mode transfer control apparatus for a hybrid vehicle. In the above-described Japanese Patent Application First Publication, the hybrid vehicle to which a power train system as will be described below is applied is disclosed. In the power train system, a brake is installed on any one of revolutional elements of a differential gear unit constituted by, for example, a planetary gear mechanism having four or more elements and two degrees of freedom, an output to a drive system being allocated to one of the other revolutional elements of the differential gear unit. In this hybrid vehicle, in a state, for example, in which the vehicle is traveling at a certain speed, a mode transfer between an electric vehicle mode (so-called, EV mode) in which a continuously variable transmission gear ratio is achieved only by a drive of two motors and an electric vehicle-low brake mode (so-called, EV-LB mode) in which the vehicle is driven by means of the two motors at a fixed transmission gear ratio with a low brake engaged is carried out.